FIG. 1 is a flowchart illustrating a network entry procedure when a user equipment (UE) is initialized in a broadband wireless access system.
(1) When initially powered on, a UE searches for a downlink channel and acquires uplink/downlink synchronization with a base station (BS). In this case, the UE acquires uplink/downlink channel parameters by receiving a downlink-MAP (DL-MAP) message, an uplink-MAP (UL-MAP) message, a downlink channel descriptor (DCD) message, and an uplink channel descriptor (UCD) message.
(2) The UE performs ranging with the BS to adjust uplink transmission parameters and receives a basic management connection identifier (CID) and a primary management CID from the BS.
(3) The UE negotiates basic capabilities with the BS.
(4) The UE executes authorization.
(5) The UE registers itself with the BS. The UE managed by an Internet Protocol (IP) receives a secondary management CID from the BS.
(6) The UE establishes IP connectivity.
(7) A current date and time are established.
(8) Constituent files of the UE are downloaded from a trivial file transfer protocol (TFTP) server.
(9) Connection for a prepared service is established.
A physical layer of a broadband wireless access system is divided into a single-carrier type and a multi-carrier type. The multi-carrier type uses orthogonal frequency division multiplexing (OFDM), and introduces orthogonal frequency division multiple access (OFDMA) as an access method capable of allocating resources in units of subchannels grouping a part of carriers.
In an OFDMA physical layer, active carriers are separated into groups and the separated carriers are transmitted to different receiving ends. A group of carriers transmitted to one receiving end is called a subchannel. Carriers constituting each subchannel may be adjacent to each other or may be separated from each other at regular intervals. Since such multiple accesses in units of subchannels are possible, a frequency diversity gain, a gain caused by concentration of power, and forward power control can be efficiently performed although complexity of implementation is increased.
A slot allocated to each user is defined by a data region of a two-dimensional time-frequency space and represents a set of successive subchannels allocated by bursts. In OFDMA, one data region is illustrated by a rectangular determined by time coordinates and subchannel coordinates. Such a data region is allocated to uplink of a specific user or, in downlink, can be transmitted by a BS to a specific user. To define the data region in two-dimensional space, the number of OFDM symbols in a time domain and the number of successive subchannels starting at a position separated from a reference point by offset should be determined.
On the other hand, the base station (BS) transmits downlink or uplink resource allocation information and a variety of control messages associated with individual operations to the user equipment (UE). The UE communicates with the base station (BS) using such messages. In this case, a method for configuring a control message and a method for transmitting the control message should be optimally designed in consideration of the whole system overhead.
When configuring such a control message, the category of the control message may be determined using a unique method for each system, and a method for transmitting a control message may be decided in various ways.
Specifically, the Institute of Electrical and Electronics Engineers (IEEE) 802.16m system classifies a control message into User Specific Control Information (USCI) and Non-User Specific Control Information (NUSCI). The USCI may be referred to as a User Specific Advanced Map (User Specific A-Map). The USCI is designed to transmit a specific-purposed control message to a specific user or group, whereas the NUSCI is designed to transmit control information to all users.
The USCI may be classified into various types according to various purposes, for example, DownLink Resource Allocation type (DL-RA type), Uplink Resource Allocation type (UL-RA type), DL-Persistent Resource Allocation type (DL-Persistent RA type), UL-Persistent Resource Allocation type (UL-Persistent RA type), power control information type, and the like. The persistent resource allocation allocates resources for a predetermined duration at intervals of a predetermined time by assigning periodic characteristics to resource allocation.
On the other hand, a user equipment (UE) needs to be assigned a separate channel for transmitting a signal such as ACK(ACKnowledgement)/NACK(Negative ACKnowledgment) so as to smoothly communicate with a base station (BS). Information regarding the separate channel allocation must be contained in the USCI. In this case, said information can be transmitted to each UE or group by a field generated at a USCI belonging to a specific type (e.g., DL-RA type) in which said information should be transmitted. However, when transmitting a control message in terms of the effective use of transmission (Tx) resources, a method for effectively transmitting said information is needed.